This invention relates generally to fasteners for joining together two or more plates, and, more particularly, to fasteners having an internally-threaded pin adapted to be guided through aligned openings in the plates and a cup-shaped accommodating element that can be tightened with the pin via a threaded bolt mounted centrally therein.
In fasteners of this particular kind, the cup-shaped accommodating element is typically provided with spring means acting opposite to the direction of entry of the pin. Two locking washers or disks are typically accommodated on the threaded bolt and engage each another when in the tightened position. The locking washer facing the pin is rotatably guided and axially displacable up to an external stop of the accommodating element, and the locking washer facing away from the pin is rotation-fast but guided in displacable fashion within the accommodating element, axially against the spring means. The pin-side locking washer, under action of a moment of rotation applied by the pin that exceeds a certain value, is rotatable relative to the locking washer facing away from the pin, whereby the pin can be screwed onto the threaded bolt up to the tightened position.
The type of fastener described briefly above is generally known. Such fasteners are used primarily for releasably fastening structural and non-structural connections that are exposed to high tension and shear stresses, as well as to vibrations. They are particularly well suited for use in aircraft, for example, in fastening cover plates, cowlings and maintenance hatches. In this particular area of application, these types of fasteners are usually exposed to a great number of load cycles, whereby individual forces can assume relatively high values. In addition, vibrations can promote loosening of fasteners of this type.
Known fasteners of this type typically further have separate locking means for preventing an unintended loosening of the fastener in the tightened condition. This commonly takes the form of two disks toothed opposite to each other. However, it has been shown in practice that load cycles and vibrations can occur so that the fastener can remain completely open, at least to the extent that the axial bias is lost. Since the fastener, besides the pure holding function in the tightened condition, is also stressed by shearing, it can loosen itself not only in the case of disappearing bias, but also by failing to transfer the shearing stresses. Another disadvantage to fastener of this type is that, because of engagement of two gears as a securing means, there ensues only a discrete clamping process, which can lead to an insufficient clamping or tightening of the plates. Furthermore, the toothed disks are relatively costly to manufacture.
It is therefore an object of the present invention to provide a fastener of the initially mentioned type that guarantees a positive transferring of stresses, assures an axial bias corresponding to the moment of rotation introduced, and guarantees an adequate clamping of the plates.